Nanocrystalline nc-3C—SiC and amorphous a-SiC layers of varying composition have been described for application in microelectronics and photovoltaics and as an oxidation protection layer. In addition to crystalline SiC layers with a cubic structure, which are referred to as beta- or 3C—SiC layers, there are also crystalline alpha-SiC layers, which can only be obtained at high temperatures above 1300° C. (C. H. Carter, V. F. Tsvetkov, R. C. Glass, D. Henshall, M. Brady, St. G. Müller, O. Kordina, K. Irvine, J. A. Edmond, H.-S. Kong, R. Sing, S. T. Allen, J. W. Palmour, Materials Science and Engineering, B61-62 (1999), 1-8). This high-temperature modification is only relevant for a few applications in microelectronics.
Hydrogenous 3C—SiC layers, which may also be nanocrystalline, are also known. A semiconductor component with hydrogen-containing microcrystalline μc-SiC:H is described in EP 1 950 810 A2. For photovoltaics, hydrogen-containing nanocrystalline nc-3C—SiC:H is used as a window layer in heterojunction solar cells (S. Miyajima, M. Sawamura, A. Yamada, M. Konagai, Journal of Non-Crystalline Solids, 354 (2008), 2350-2354). Such layers are characterized by a high hydrogen content, which rules out their application as a wear protection layer if temperatures are above 500° C. (A. K. Costa, S. S. Camargo, Surface and Coatings Technology, 163-164 (2003), 176-180).
Hydrogen-free SiC possesses high oxidation resistance and is therefore also used as an oxidation protection layer (H. Jian-Feng, L. Miao, W. Bo, C. Li-Yun, X. Chang-Kui, W. Jian-Peng, Carbon, 47 (2009), 1189-1206).
SiC has rarely been used to date as a wear protection layer on tools and structural components. The reasons are its high brittleness (H. O. Pierson, Handbook of Refractory Carbides and Nitrides, NOYES Publications, Westwood, N.J., U.S.A., 1996) and its reactivity with ferrous materials at high temperatures (R. C. Schiepers, J. A. van Beek, F. J. J. van Loo, G. de With, Journal of the European Ceramic Society, 11 (1993), 211-218). Only in U.S. Pat. No. 3,011,912 and two references in the literature concerning the patent is there any mention of possible applications of crystalline or amorphous SiC layers as wear protection layers. A process is described for the manufacture of beta-SiC layers on inorganic substrates. These layers contain no chlorine, as chlorine-free starting materials are used. A wear-reducing protective layer on a very special structural component, namely gramophone needles, is given as a possible application. There is no mention of the exact structure and properties of the beta layer.
The manufacture of crystalline 3C—SiC layers with crystallite sizes of >0.3 μm on hard metal substrates is described in a scientific publication (G. Giunta, M. Fiorini, V. Vittori, G. Marchesano, Surface and Coatings Technology, 49 (1991), 174-180). A CVD process is described that uses methyltrichlorosilane at a temperature of 1000° C. Because of the high coating temperature, direct coating of hard metals is not possible. Harmful cobalt silicides are formed, and bond strength is insufficient. Hard metal can only be coated using complex intermediate layer systems that act as diffusion barriers.
A pure amorphous SiC layer on a hard metal tool is described by which reduction of abrasive wear was confirmed as measured by a tribometer test at up to 700° C. in A. K. Costa, S. S. Camargo, Surface and Coatings Technology, 163-164 (2003), 176-180.
Nanocrystalline and amorphous SiC layers, although they consist of sintered particles or clusters with a size of 50 nm to 500 nm and thus do not possess a homogeneous structure and composition, can be manufactured using the DC plasma jet CVD process (J. Wilden, A. Wank, Galvanotechnik 91 (2000), No. 8, 2250-2256). However, if chlorine-containing standard starting materials are used in that process such as trimethylchlorosilane or trichloromethylsilane, the layer will show chlorine concentrations that are so high that they adversely affect the described coating of steels and metals. The chlorine concentration is particularly high in the interface area to the substrate.
It could therefore be helpful to provide bodies with SiC layers that possess a particle-free, non-porous structure, a high degree of hardness, low brittleness, high bond strength, good oxidation resistance, and a high resistance to crack growth.